The field of this invention relates to a wireless communication unit, a frequency conversion circuit and method for frequency and phase conversion, and in particular to a frequency conversion circuit with a programmable duty cycle.
In telecommunications, there has been a recent trend for device manufacturers to design wireless communication units that are capable of operating over multiple frequency bands, to enable the same device to operate in different geographical regions, as well as being able to switch between different service providers and different communication technologies. The term ‘multi-band device’ for example, is one that encompasses dual-band, tri-band, quad-band and penta-band devices, and is typically a wireless/mobile phone communication device that supports multiple radio frequency bands. All wireless/mobile phone communication devices that support communications on more than one channel use multiple frequencies. However; a band is a group of frequencies containing many channels. Where the bands are widely separated in frequency, parallel transmit and receive signal path circuits must be provided, which increases the cost, complexity and power demand of multi-band devices.
Hence, in the field of radio frequency (RF) communication units, architectures for supporting communications across multiple and various frequencies have been developed. Typically, a single architecture is able to support multiple frequencies through provision of variable, programmable, duty cycles of the frequency generation signals. For example, 25% duty cycles are common for most cellular transmitters, and architectures providing 33% duty cycles are common for long term evolution (LTE™) communication bands 13 and 26.
Referring to FIG. 1, known examples of a 25% duty cycle architecture 100, and a 33% duty cycle architecture 140, together with a module combining the operation of 25% duty cycle and 33% duty cycle operations 160 are illustrated.
Referring to the 25% duty cycle architecture 100, a series of phase shifted signals are ‘mixed’ with digital, quadrature-based, baseband signals in order to compensate for varying phase shifts before a resultant RF signal is output at 130. In this case, a baseband signal (BB-0) 102 may have a zero phase shift and, therefore, a local oscillator reference signal (LO-0) with a zero phase shift 104 may be combined or mixed with digital baseband signal 102 to produce a zero phase shift output. Another digital baseband signal (BB-90) 106 has a quadrature phase shift of 90 degrees and, therefore, when mixed with a local oscillator reference signal (LO-270) with a 270 degree phase shift 108 produces a radio frequency signal of a zero phase shift. A similar procedure is carried out for the remaining digital baseband signals BB-180 and BB-270, when mixed with LO-180 and LO-90 in the 25% duty cycle architecture 100.
Referring to the 33% duty cycle architecture 140, a similar operation to that described with relation to the 25% duty cycle architecture 100 is carried out for the 33% duty cycle architecture. However, in this case, there are only three digital baseband signals (BB-0, BB-180 and BB-270) to quadrature frequency convert with corresponding, respective local oscillator reference signal (LO-0, LO-240 and LO-120), due to the increased duty cycle of 33%.
Associated timing diagrams 110 and 150 illustrate the respective phase shifts of the local oscillator reference signals.
It is known that, in some instances, the 25% duty cycle architecture 100 and 33% duty cycle architecture 140 can be combined together to form a further module 160, operable to switch between different duty cycle operations via multiplexer 164, thereby providing a more flexible duty cycle generation module 160 that may support a wider range of frequencies and/or communication standards. In this instance, any of four digital baseband signal (BB-0, BB-90, BB-180, BB-270) 162 may be mixed/combined with any of seven respective local oscillator reference signals 164.
However, as illustrated, in order to achieve this more flexible duty cycle generation module 160, a significant duplication of hardware is required. In the illustrated case, in order to implement a combined 25% and 33% duty cycle operation, seven mixers 162 and a multiplexer 164 are required.
In some examples, it may be beneficial to provide a system that is operable to supply at least two different frequency shifted and phase shifted duty cycle regimes, whilst reducing the number of hardware components required.